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L0301P79 - Healing and Repair
Consequences of Cell Injury *reversible = regernation or adaptation *irreversible = repair Outcomes of Response to Injury *resolution **regeneration **repair by tissue adaptation *chronic inflammation *scarring **repair by fibrous tissue Resolution *may occur when: **injury limited or short term **tissue damage minimal or absent **tissue is capable of regenerating *begins after: **acute inflammatory responses have finished Scarring *may occur when: **tissue destruction is substantial **tissue is not capable of regenerating **following chronic inflammation Healing of Skin Wounds *cutaneous wound healing involves: **epithelial regeneration **formation of connective tissue scar *depending upon nature and size of wound healing is by: **first intention **second intention Wound-Healing Process #haemostasis - clotting #inflammation #proliferation #remodelling - rebuilding *EPC - endothelial progenitor cells Healing by First Intention *example: clean, uninfected surgical incision *skin is held together to allow healing **naturally by a weak fibrin join **medically by sutures Skin Recovery After Suturing *well sutured = ~70% strength of normal skin *suture removal usually after one week - strength approx. 10% *strength increases rapidly over next the next month - increases to 70-80% after 3 months *usually does not increase much beyond this   Factors Affecting Healing *age *infection *diabetes and obesity *poor knotting of surgical stitches *collagen disorders *additional stress on wound Healing by Second Intention *large wounds - cell/tissue loss is extensive: **deep lacerations **extensive burns **abscess formation **ulceration **ischaemic necrosis (infarction) in parenchymal organs *combination of regeneration and scarring **wound edge do not approximate (come together) **phagocytosis to remove debris **formation of granulation tissue **epithelial regeneration to cover surface ***generally puckered and contracted skin Formation of Granulation Tissue *capillary endothelial cells proliferate and grow into the area *solid buds of cells open into vascular channels (blood vessels) and arranged as loops into the damaged area *proliferation and stimulation of fibroblasts to  become myofibroblasts which produces fibrin and releases it into the tissue Organisation *myofibroblasts contract **granulation tissue contracts, reducing volume of tissue for repair *collagen accumulates to form fibrous tissue scar Collagen Production *collagen is a fibrous protein between cells, that provides strength to tissues *a few days after injury, fibroblasts begin proliferation in the site of injury and secrete collagen, which forms a strong scar *over weeks to months, collagen is remodelled and partially resorbed as the tissue attempts to return to normal structure and function   Healing and Repair in the GIT Mucosal Erosion *similar to first intention skin healing *loss of part of the thickness of mucosa *viable epithelial cells next to damaged area can rapidly replicate to replace missing cells *full regeneration of epithelium Mucosal Ulceration *loss of full thickness of mucosa *can involve deeper layers (muscularis propria) *phases of healing: **haemostasis ***thin layer of fibrin on surface **inflammation **formation of granulation tissue **regeneration of mucosal epithelium on surface *leaves an underlying layer of scar tissue under puckered epithelial tissue *example: peptic ulcer **injury in the stomach **persistent and ongoing inflammation **ongoing repair **area will not regain normal function Healing and Repair of Bone *haemostasis ***formation of haematoma (swelling of clotted blood) at fracture site **splints are required to hold the fractured bone in place for correct formation **if not in the correct place, surgery to reposition edges of the broken bone *inflammation **removal of debris and bone fragments *organisation of haematoma to form cartilage callus (fibroblasts and osteoblasts) *remodelling of callus to produce new bone Process #formation of fracture haematoma #formation of callus #cartilage of callus is replaced by bone #remodelling of bone to its as close to the original normal size Factors Affecting Fracture Healing *delay or arrest of repair can result from: **movement **gross misalignment **interposed soft tissue ***soft tissue between bone fragments **infection **pre-existing bone disease Factor Affecting Tissue Repair *infection *nutrition, especially vitamins *glucocorticoids **steroids with anti-inflammatory effects *mechanical variables, especially movement *poor perfusion **poor movement of materials within wound *foreign bodies **particularly accidents - glass, metal *location of injury and stress on injury site *aberrations of cell growth Summary *outcome depends upon *size and extent of injury *type of tissue involved *persistence of injurious agent *host factors